1. Field of the Invention
This invention relates to a device for the directionally-dependent influencing or control of the flow velocity of the fluid in hydraulic actuator systems, in particular of friction clutches in motor vehicles, with a throttle which is located between a master cylinder and a slave cylinder in the hydraulic system, which throttle is formed by a base body with at least one passage hole which can be at least partly closed.
2. Background Information
Hydraulic actuator devices for friction clutches are widely known. These devices consist of a master cylinder which can be pressurized by means of the clutch pedal and a slave cylinder which is connected to the master cylinder via a hydraulic line, which slave cylinder actuates the friction clutch by means of a release mechanism.
When the clutch is released, hydraulic fluid flows from the master cylinder into the slave cylinder, as a result of which the clutch opens. That is, when the clutch pedal is pushed down, hydraulic fluid flows from the master cylinder into the slave cylinder, as a result of which the clutch is disengaged. If the clutch pedal is released, the hydraulic fluid flows from the slave cylinder back into the master cylinder and the clutch is closed or engaged. If the clutch pedal is released when the vehicle is travelling extremely fast, for example if the driver's foot slips off the clutch pedal, the hydraulic fluid flows rapidly back out of the slave cylinder, as a result of which there is a hard clutch engagement, and extreme peak torques can occur which can be several times higher than the engine torque. Similarly, if the clutch pedal is released when the motor is running at a high speed, for example if the driver's foot slips off the clutch pedal, the hydraulic fluid flows rapidly back out of the slave cylinder, as a result of which there is a hard clutch engagement, and extreme peak torques can occur which can be several times higher than the engine torque. These peak torques cause a correspondingly high load on the drive train and result in a corresponding amount of wear.
To prevent the sudden closing or engaging of the clutch, German Patent No. 37 36 584 A1, for example, describes a device similar to the one described above in the hydraulic line between the master cylinder and the slave cylinder. For this purpose, there is a piston in a housing, which piston is mounted so that it can be displaced axially and has a central through hole and a plurality of axial peripheral grooves, and is held in its open position by means of a pressure spring or compression spring. When the clutch is released, the hydraulic fluid coming from the master cylinder flows unrestricted through the central through hole and the peripheral grooves toward the slave cylinder. If the clutch pedal is suddenly released, the pressure on the spring-loaded piston increases, and the piston moves axially toward the housing wall, as a result of which the peripheral grooves are closed and the hydraulic fluid can flow back only via the central through hole, as a result of which there is a corresponding delay in the closing or engaging of the clutch.
One disadvantage of this realization is that the viscosity of the hydraulic fluid changes during the operation of the motor vehicle. When the outside temperature is low, the viscosity of the hydraulic fluid is correspondingly high. The flow velocity of the fluid is therefore influenced fundamentally by the throttle in both directions. But there are situations in which the throttling action is too high during the return flow, and the clutch cannot follow the path specified by the operator in normal operation. The clutch pedal consequently remains "stuck" or "hangs." Although the driver has already deliberately released the clutch pedal, the clutch is not yet fully engaged. Because normally, the engine speed increases immediately after the driver releases the clutch pedal, there is a corresponding wear on the friction linings of the clutch. The delayed response of the clutch also reduces the ride comfort. The flow cross section can be made larger, but that can have the consequence that at high temperatures and thus correspondingly lower viscosities of the hydraulic fluid, the throttling action is no longer sufficient, and under extreme conditions, peak torques can be transmitted into the drive train.
Modern vehicles must be designed so that they can be operated worldwide under all climatic conditions. Therefore, it must be possible to operate the vehicle both in Arctic winters at the poles and in hot desert summers, without having to use special components.